Transposable elements have been used in simpler biological systems to clone genes of interest by virtue of the fact that insertion of a transposable element may cause a mutation at the site of integration ("transposon tagging"). To investigate the feasibility of using murine retroviruses as tagged insertional mutagens, I am collaborating with Dr. Cindy Edwards in an attempt to clone the gene for the aryl hydrocarbon (Ah) receptor using a modified Mo-MuLV as the tagged mutagen. Cells containing a single functional copy of the Ah receptor were infected with Mo-MuLV and over 20 mutant cell lines lacking the Ah receptor were selected. We cloned integrated copies of Mo- MuLV along with flanking cellular DNA from these cell lines. Several clones from different cell lines appear to contain a copy of Mo-MuLV integrated in the same fragment of cellular DNA. Further analysis of these cellular DNA fragments is underway. Significance: These experiments represent an attempt to clone an important gene involved in the metabolism of aryl hydrocarbons, and provide a model system for the use of retroviruses as "tagged transposons" to clone selectable genes in higher eukaryotes.